/*
       * INET		An implementation of the TCP/IP protocol suite for the LINUX
       *		operating system.  INET is implemented using the  BSD Socket
       *		interface as the means of communication with the user level.
       *
       *		Pseudo-driver for the loopback interface.
       *
       * Version:	@(#)loopback.c	1.0.4b	08/16/93
       *
       * Authors:	Ross Biro, <bir7@leland.Stanford.Edu>
       *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
       *		Donald Becker, <becker@cesdis.gsfc.nasa.gov>
       *
       *		Alan Cox	:	Fixed oddments for NET3.014
       *		Alan Cox	:	Rejig for NET3.029 snap #3
       *		Alan Cox	: 	Fixed NET3.029 bugs and sped up
       *		Larry McVoy	:	Tiny tweak to double performance
       *		Alan Cox	:	Backed out LMV's tweak - the linux mm
       *					can't take it...
       *              Michael Griffith:       Don't bother computing the checksums
       *                                      on packets received on the loopback
       *                                      interface.
       *		Alexey Kuznetsov:	Potential hang under some extreme
       *					cases removed.
       *
       *		This program is free software; you can redistribute it and/or
       *		modify it under the terms of the GNU General Public License
       *		as published by the Free Software Foundation; either version
       *		2 of the License, or (at your option) any later version.
       */
      #include <linux/kernel.h>
      #include <linux/sched.h>
      #include <linux/interrupt.h>
      #include <linux/fs.h>
      #include <linux/types.h>
      #include <linux/string.h>
      #include <linux/socket.h>
      #include <linux/errno.h>
      #include <linux/fcntl.h>
      #include <linux/in.h>
      #include <linux/init.h>
      
      #include <asm/system.h>
      #include <asm/uaccess.h>
      #include <asm/io.h>
      
      #include <linux/inet.h>
      #include <linux/netdevice.h>
      #include <linux/etherdevice.h>
      #include <linux/skbuff.h>
      #include <net/sock.h>
      #include <linux/if_ether.h>	/* For the statistics structure. */
      #include <linux/if_arp.h>	/* For ARPHRD_ETHER */
      
      #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
      
      /*
       * The higher levels take care of making this non-reentrant (it's
       * called with bh's disabled).
       */
  61  static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
      {
      	struct net_device_stats *stats = (struct net_device_stats *)dev->priv;
      
      	/*
      	 *	Optimise so buffers with skb->free=1 are not copied but
      	 *	instead are lobbed from tx queue to rx queue 
      	 */
      
  70  	if(atomic_read(&skb->users) != 1)
      	{
      	  	struct sk_buff *skb2=skb;
      	  	skb=skb_clone(skb, GFP_ATOMIC);		/* Clone the buffer */
  74  	  	if(skb==NULL) {
      			kfree_skb(skb2);
  76  			return 0;
      		}
      	  	kfree_skb(skb2);
      	}
  80  	else
      		skb_orphan(skb);
      
      	skb->protocol=eth_type_trans(skb,dev);
      	skb->dev=dev;
      #ifndef LOOPBACK_MUST_CHECKSUM
      	skb->ip_summed = CHECKSUM_UNNECESSARY;
      #endif
      	netif_rx(skb);
      
      	stats->rx_bytes+=skb->len;
      	stats->tx_bytes+=skb->len;
      	stats->rx_packets++;
      	stats->tx_packets++;
      
  95  	return(0);
      }
      
  98  static struct net_device_stats *get_stats(struct net_device *dev)
      {
 100  	return (struct net_device_stats *)dev->priv;
      }
      
      /* Initialize the rest of the LOOPBACK device. */
 104  int __init loopback_init(struct net_device *dev)
      {
      	dev->mtu		= PAGE_SIZE - LOOPBACK_OVERHEAD;
      	dev->hard_start_xmit	= loopback_xmit;
      	dev->hard_header	= eth_header;
      	dev->hard_header_cache	= eth_header_cache;
      	dev->header_cache_update= eth_header_cache_update;
      	dev->hard_header_len	= ETH_HLEN;		/* 14			*/
      	dev->addr_len		= ETH_ALEN;		/* 6			*/
      	dev->tx_queue_len	= 0;
      	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001		*/
      	dev->rebuild_header	= eth_rebuild_header;
      	dev->flags		= IFF_LOOPBACK;
      	dev->priv = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
 118  	if (dev->priv == NULL)
 119  			return -ENOMEM;
      	memset(dev->priv, 0, sizeof(struct net_device_stats));
      	dev->get_stats = get_stats;
      
 123  	if (num_physpages >= ((128*1024*1024)>>PAGE_SHIFT))
      		dev->mtu = 4096*4 - LOOPBACK_OVERHEAD;
      
      	/*
      	 *	Fill in the generic fields of the device structure. 
      	 */
         
      	dev_init_buffers(dev);
        
 132  	return(0);
      };